Problem: Kevin is 2 times as old as Nadia. 24 years ago, Kevin was 8 times as old as Nadia. How old is Kevin now?
Answer: We can use the given information to write down two equations that describe the ages of Kevin and Nadia. Let Kevin's current age be $k$ and Nadia's current age be $n$ The information in the first sentence can be expressed in the following equation: $k = 2n$ 24 years ago, Kevin was $k - 24$ years old, and Nadia was $n - 24$ years old. The information in the second sentence can be expressed in the following equation: $k - 24 = 8(n - 24)$ Now we have two independent equations, and we can solve for our two unknowns. Because we are looking for $k$ , it might be easiest to solve our first equation for $n$ and substitute it into our second equation. Solving our first equation for $n$ , we get: $n = k / 2$ . Substituting this into our second equation, we get: $k - 24 = 8($ $(k / 2)$ $- 24)$ which combines the information about $k$ from both of our original equations. Simplifying the right side of this equation, we get: $k - 24 = 4 k - 192$ Solving for $k$ , we get: $3 k = 168$ $k = \dfrac{1}{3} \cdot 168 = 56$.